1. Field of the Invention
This invention relates to an electronic device in a thin film form, the method of its manufacture, and a sputtering target. Specifically the invention relates to a novel display device comprising, as its constituents, pixel electrodes used in active and passive matrix type flat panel displays such as semiconductor displays and liquid crystal displays, reflective films, optical components etc., and aluminum alloy film; the method of its manufacture; and the sputtering target.
2. Description of the Related Art
For example, the active matrix type liquid crystal display uses thin film transistors (TFT) as switching elements, and is composed of a TFT array substrate equipped with a wiring section of pixel electrodes, scan lines, signal conductors, etc., an opposed substrate equipped with a common electrode that is disposed in opposition to the TFT array substrate with a predetermined spacing, and a liquid crystal layer that is filled between the TFT array substrate and the opposed substrate. For the pixel electrodes, an indium tin oxide (ITO) film with about 10 wt % tin oxide (SnO) contained in indium oxide (In2O3) and the like is used.
Moreover, regarding the signal conductors of the wiring section that are connected to these pixel electrode electrically, in order that pure aluminum or an aluminum alloy, such as Al—Nd, shall not come in direct contact with the pixel electrodes, a multilayer film made of a high melting point metal, such as Mo, Cr, Ti, and W, is made to exist between them as a barrier metal. However, recently, trials where these high melting point metals are eliminated and the pixel electrode is brought into direct connection with the signal conductor are being advanced.
For example, according to JP-A No. 337976/1999, it is described that if a pixel electrode made of an ITO film with about 10 wt % zinc oxide contained in indium oxide is used, direct contact with signal conductors becomes possible.
Moreover, U.S. Pat. No. 6,218,206 discloses a method of performing surface treatment on a drain electrode by plasma processing or ion implantation, and U.S. Pat. No. 6,252,247 discloses a method of forming a multilayer film by depositing a second phase containing impurities, such as N, O, Si, and C, on a first layer of gate, source, and drain electrodes on the first layer of gate, source, and drain electrodes. It was made clear that adoption of these methods makes it possible to maintain contact resistance with the pixel electrode to a low level even if the high melting point metal is eliminated.
The reason for disposing a barrier metal in-between in the conventional technology is that, if aluminum or aluminum alloy wiring that constitutes signal conductors is brought into direct contact with the pixel electrode, the contact resistance will increase and display quality of a screen will deteriorate. This is because aluminum is very easy to oxidize and the surface thereof is easily oxidized in the air and because the pixel electrode is a metal oxide and hence aluminum is oxidized by oxygen generated at the time of film deposition and oxygen added at the time of film deposition to form an aluminum oxide layer on the surface thereof. Then, if an insulating material layer is formed in the contact interface between the signal conductors and the pixel electrode in this way, the contact resistance between the signal conductors and the pixel electrode will increase and the display quality of a screen will deteriorate.
On the other hand, although the barrier metal has originally an action of preventing surface oxidization of the aluminum alloy and improving contact between the aluminum alloy film and the pixel electrode, a barrier metal forming process becomes indispensable to obtain the conventional structure wiring such that a barrier metal is disposed between the contact interface; therefore, a deposition chamber for forming a barrier metal must be provided redundantly in addition to a depositing sputtering apparatus required for the formation of the gate electrode, the source electrode, and the drain electrode. However, as the cost of a liquid crystal panel etc. keeps to be reduced by mass production, it has become difficult to neglect the increase in the manufacturing cost and the decrease in productivity accompanying the formation of a barrier metal.
Due to such circumstances, an electrode material and a manufacturing process that enables dispensing of the barrier metals are desired recently. In response to such a demand, U.S. Pat. No. 6,218,206 supplemented one process for performing surface treatment. On the other hand, according to U.S. Pat. No. 6,252,247, deposition of the gate electrode, the source electrode, or the drain electrode can be performed continuously in the same deposition chamber, but increase in the number of steps cannot be avoided. Besides, when the chamber is used continuously, there occurs frequently a phenomenon that films peel off the wall of the chamber due to a difference of thermal expansion coefficient between a film into which impurities have been mixed and a film into which no impurity has been mixed, and consequently the equipment must be halted frequently because of maintenance. Moreover, according to the patent document 1, indium tin oxide (ITO) that is most popular at present must be altered to indium zinc oxide (IZO), which increases material cost.
In order to maintain the display quality of a display device, the electrode material is required to provide low electric resistance and a high level of heat resistance. For example, the properties required to be used as a source and drain electrode material of the amorphous TFT (one of elements of display devices) etc. are an electrical resistivity of 8 μΩ·cm or less (preferably, 5 μΩ·cm or less) and a heatproof temperature of 300 to 350° C. The properties required to be used as a gate electrode material are an electrical resistivity of 8 μΩ·cm or less and a heatproof temperature of 400 to 450° C. Since a current is made to flow always in the source/drain electrodes in order to read a pixel, it is desirable to suppress the electrical resistivity low and hence lessen power consumption of the display device. Moreover, it is necessary to lessen the time constant that is determined as a product of resistance and regulation capacity, so that display quality can be maintained even when the display panel is enlarged. Furthermore, the required heat resistance varies with the structure of a display device, and depends on deposition temperature of an insulating film that is used in post processing after electrode formation, and deposition temperature and heat treatment temperature of semiconductor layers.